This invention relates to devices for deriving useful work from the controlled combustion of fuels within the device. More specifically, it relates to an internal combustion system that avoids a rigid piston movable within a rigid cylinder to convert the combustion energy into either a mechanical or hydraulic output.
One of the most widely used sources of mechanical power, particularly portable power sources, is the internal combustion engine. In all of its commercial forms, this engine is characterized by a rigid piston or piston-like member that moves within a rigid cylinder, or a comparable structure. In standard Otto-cycle four stroke engine, a generally cylindrical piston reciprocates within a cylindrical bore (cylinder) in an engine block. A crankshaft converts the reciprocating motion into a rotary output torque. Valves and a spark plug are mounted at one end of the cylinder. The basic approach is the same for diesel engines, except ignition is produced through the compression of a fuel-oxidizer mixture without the use of a sparkplug. In the last century the only radical departure in the design of the internal combustion engine wa the Wankel rotary engine. A rigid rotating piston replaces the reciprocating piston. A rigid surrounding chamber with a generally elliptical shape functions as the cylinders. An output shaft is connected directly to the rotating "piston".
All of these known engines address competing design consideration, and have limitations inherent in the common aspects of their solution to these design problems. Any internal combustion engine produces a significant level of heat of the combustion. Rigid moving parts must be able to resist the heat and to operate over a wide range of temperatures, from a cold start to very high temperatures during normal operation. The engine must have a cooling system that effectively dissipates the heat of combustion before it builds to levels that are destructive of the engine. It is also necessary to seal one rigid part that moves with respect to another rigid part in a high temperature, dirty and generally hostile environment. Wear of the seal is an important factor in the performance and product life of standard Otto-cycle engines, and a major reason why Wankel rotary engines have not supplanted the Otto-cycle engines in powering automobiles. Friction at the seal also reduces efficiency. Lubrication of the moving parts and seals is essential to reduce friction and control wear. Also, the rigid moving parts must closely match in dimension and be manufactured to close tolerances, which is reflected in increased manufacturing costs.
The operation of the engine also requires a mechanical coupling of the movement of the piston to an output shaft and a mechanism for coordinating the movement of the piston with the operation of valves to control the introduction of fuel and an oxidizer to the cylinder and an exhaust of the combustion products. For Otto-cycle and Wankel engines, the coordination includes a firing of a spark plug to initiate the combustion.
The solution of a rigid piston-moving-in a rigid cylinder has certain inherent drawbacks. As noted above, rigid elements moving against one another require special seals, close tolerancing, lubrication over the surfaces in moving contact, and are susceptible to wear. Second, the material used to form conventional rigid pistons and cylinders, usually a form of steel, limit the operating temperature of the engine to a lower range than is desirable for maximum efficiency and the production of the lowest amount of objectionable products of combustion (pollution). Third, in any engine where a piston reciprocates, the mass of the piston is a source of inefficiency since some percentage of the energy produced by the combustion is used to reverse its direction of movement and accelerate the mass of the piston or pistons. The greater the mass, the greater the inherent energy loss within the engine.
Mass is also a factor in containing the internal combustion. An engine block for a cylinder or cylinders must be able to withstand the explosive force and heat of the combustion. Typically, this means forming each cylinder as a bore in a large, heavy block of metal. The weight of the block is a major component in the overall weight of an engine and a major drawback for engines and used to power a vehicles such as automobiles or airplanes. Further, conventional rigid pistons must be mechanically coupled to a power output, typically a rotating crankshaft. To obtain a hydraulic or pneumatic output, the internal combustion engine is typically used to drive a separate piece of equipment such as a compressor.
It is therefore a principal object of this invention to provide an internal combustion system that requires no special seals, exhibits excellent wear resistance, and requires no special lubrication for a member moving in response to the internal combustion.
Another principal object of this invention is to provide an internal combustion system with the foregoing advantages and which is inherently and automatically well cooled.
A further principal object is to provide an internal combustion system that can operate at higher combustion temperatures than are possible with conventional engines to increase the efficiency of the system and reduce the emission of environmentally harmful combustion products.
Still another advantage of the invention is to provide a system that is easily maintained and has a low weight as compared to similarly rated conventional rigid piston engines.
Another advantage of the present invention is that the part or parts responding to the combustion do not have to be machined to close tolerances and can be formed, at least in part, from component materials that exhibit low densities, good wear and heat resistance, and have favorable costs of manufacture.
Yet another advantage of the present invention is that the energy of the fuel combustion can be converted directly into either hydraulic output or a mechanical output.
A still further advantage is that the internal combustion system of the present invention can be readily assembled in modules to tailor the capacity of the engine.